[fpc-pascal] Re: Delphi's anonymous functions in Free Pascal

[Florian Klämpfl]

Am 05.11.2011 22:58, schrieb Alexander Shishkin:
> 06.11.2011 1:46, Michael Van Canneyt пишет:
>>
>>
>> On Sat, 5 Nov 2011, Bernd wrote:
>>
>>> 2011/10/25 <michael.vancanneyt at wisa.be>:
>>>
>>>>> targethread.queue(
>>>>>  procedure(targetobject:ttargetobject;a:integer;b:someobject;c:string)
>>>>>             begin
>>>>>               targetobject.destinationprocedure(a,b,c);
>>>>>             end;
>>>>>
>>>>> Note how common this looks compared to the original.
>>>>
>>>> One point is that you could do the above with a local (and named)
>>>> procedure
>>>> as well, and still have all the context. At the very least you would
>>>> not be
>>>> raping pascal's readability by putting a
>>>> complete procedure declaration inside a code block.
>>>
>>> How would you preserve the context without finding some place
>>> somewhere (on the heap) to store the current values of a, b, and c?
>>>
>>
>> Procedure SomeOuter;
>>
>> Var
>> d,e,f : SomeType;
>>
>> Procedure
>> SomeInner(targetobject:ttargetobject;a:integer;b:someobject;c:string)
>>    begin
>>      targetobject.destinationprocedure(a,b,c);
>>    end;
>>
>> begin
>> Targethread.queue(@SomeInner(aobject,d,e,f));
>> end;
>>
>> No difference with 'closure', except more readable.
>>
> 
> Closures can be returned as a function result but nested procedure not
> (more strictly, this can be complied but will not work because of
> lifetime of nested procedure).

Of course, but what Michael means is: closure support does not require
necessarily anonymous proceudures/functions/methods.

It would be probably more clear to write and this more pascalish:

Procedure SomeOuter;

Var
  d,e,f : SomeType;

  Lambda Procedure
SomeInner(targetobject:ttargetobject;a:integer;b:someobject;c:string)
  begin
     targetobject.destinationprocedure(a,b,c);
  end;

begin
  Targethread.queue(@SomeInner(aobject,d,e,f));
end;

We don't need lambda expressions after all to implement controll
statements like e.g. smalltalk.